The present invention relates to an improved process for preparing benzenesulfonate salts of the formula (I): EQU RCO.sub.2 CH.sub.2 CO.sub.2 PhSO.sub.3 M (I).
More particularly, the present invention relates to an improved process for preparing alkanoyloxyacetyloxybenzenesulfonate salts of formula (I), wherein SO.sub.3 M is in the 4-position, from phenyl esters of acyloxyacetic acids (alkanoyloxyacetyloxybenzenes) of formula (II), by first sulfonating the phenyl ester and then neutralizing the intermediate sulfonic acid of formula (III): EQU RCO.sub.2 CH.sub.2 CO.sub.2 Ph (II) EQU RCO.sub.2 CH.sub.2 CO.sub.2 PhSO.sub.3 H (III)
Alkanoyloxyacetyloxybenzenesulfonate salts of formula (I) are known bleach activators and are described in greater detail in U.S. Pat. No. 4,778,618. The subject alkanoyloxyacetyloxybenzenesulfonate salts are conventionally prepared from the corresponding alkanoyloxyacetic acids by conversion to the corresponding acid chlorides followed by reaction with a salt of 4-hydroxybenzenesulfonic acid (i.e., 4-hydroxybenzenesulfonic acid, sodium salt) as taught in U.S. Pat. No. 4,778,618. Alternatively, salts of formula (I) may be prepared from salts of 4-(chloroacetyloxy)benzenesulfonic acid and alkanoic acids as described in U.S. Pat. No. 4,985,180. Thus, known processes for the preparation of compounds of formula (I) require the intermediacy of salts of 4-hydroxybenzenesulfonic acid. In practice, these processes can be complicated by the fact that alkali metal and alkaline earth metal salts of 4-hydroxybenzenesulfonic acid are relatively high melting solids with poor solubility in many commonly employed organic solvents.
The process of the present invention does not require a pre-formed salt of 4-hydroxybenzenesulfonic acid and is an all liquids process until the final step of neutralization which yields the solid product.
Phenyl esters of simple alkanoic acids are known to sulfonate on the aromatic ring as shown in Equation 1. ##STR1##
U.S. Pat. No. 4,588,533 describes a process for preparing acyloxybenzenesulfonic acids and the corresponding salts of formula (IV) wherein R is a hydrocarbyl radical containing up to about 30 carbon atoms and is selected from alkyl, alkenyl, cycloalkyl, aryl, aralkyl and alkaryl, and M is an alkali metal or an alkaline earth metal. In the first step of this process an acyloxybenzene is sulfonated with sulfur trioxide to give the acyloxybenzenesulfonic acid which is then neutralized with an alkali metal or an alkaline earth metal base to give the acyloxybenzenesulfonate salt of formula (IV). ##STR2##
German Patent Application 3,530,101 discloses a continuous process for the preparation of acyloxybenzenesulfonate salts of formula (V) wherein R is an aliphatic hydrocarbon which can contain from 1 to 17 carbon atoms, Y is hydrogen or an alkyl group containing from 1 to 18 carbon atoms and M is an alkali metal, an alkaline earth metal or substituted ammonium. In the first step of this process liquid acyloxybenzene is sulfonated with 0.9 to 1.3 molar equivalents of gaseous sulfur trioxide at 20.degree.-200.degree. C. and then held at 20.degree.-70.degree. C. for 5 to 180 minutes prior to being neutralized to give the acyloxybenzenesulfonate salts of formula (V). ##STR3##
U.S. Pat. No. 4,692,279 discloses a process for preparing acyloxybenzenesulfonate salt by contacting acyloxybenzene with sulfur trioxide at a temperature ranging from about -20.degree. to 50.degree. C. to produce an intermediate reaction product which comprises about a 1:1 molar adduct of the sulfur trioxide and the acyloxybenzene, which is then digested at 25.degree. to 75.degree. C. for 0.1 to 4 hours prior to neutralization which then gives the acyloxybenzenesulfonate salt. The digestion step is described as being useful for controlling the exothermic rearrangement of the sulfur trioxide-acyloxybenzene adduct. Acyloxybenzenes are normally described as being of the formula (VI) where R is a saturated aliphatic group containing from about 2 to 19 carbon atoms inclusive. ##STR4##
U.S. Pat. No. 4,695,412 discloses a process for preparing acyloxybenzenesulfonic acids of formula (VII) and their alkali metal and alkaline earth metal salts wherein R is a straight-chain or branched saturated alkyl of from 5 to 11 carbon atoms. In the first step of this process a phenyl ester is sulfonated with sulfur trioxide or chlorosulfonic acid in a molar ratio of about 1:1 in the presence of 0.2 to 30 mole % (based on sulfur trioxide or chlorosulfonic acid) of a complexing agent for sulfur trioxide or chlorosulfonic acid. ##STR5##
U.S. Pat. No. 4,588,531 discloses a continuous process for neutralizing acyloxybenzenesulfonic acids of formula (VII) wherein R is a saturated or unsaturated alkyl radical of from 1 to 17 carbon atoms or is phenyl which is unsubstituted or monosubstituted or disubstituted by alkyl of from 1 to 3 carbon atoms, halogen, methoxy or nitro, to give the corresponding alkali metal and alkaline earth metal salts. In this process the liquid acyloxybenzenesulfonic acid and 5 to 50% strength by weight aqueous solution of an alkali metal or alkaline earth metal hydroxide, carbonate, or bicarbonate are simultaneously added into water at 0.degree. to 60.degree. C. with the pH of the water/reaction medium being maintained from 2.5 to 7.0. The salts are then isolated from the aqueous solutions using conventional techniques.
U.S. Pat. No. 4,788,316 discloses a process for preparing sulfonated esters and carbonates of formula (VIII) wherein R is a C.sub.1 -C.sub.18 normal alkoxyl radical; X.sub.1 -X.sub.4 may be hydrogens or one or more may be halogens, C.sub.1 -C.sub.4 alkyl or alkoxyl radicals, RCOO-- wherein R is defined as above, or SO.sub.3 M; and M is an alkali metal, alkaline earth metal or ammonium group. The process consists of (1) preparing the unsulfonated ester; (2) sulfonating the ester; and (3) neutralizing the resulting aromatic ester sulfonic acid. This disclosure teaches that high yields of acyloxybenzenesulfonates can be obtained if the neutralization is carried out in a non-aqueous organic solution with an alkali metal, alkali earth metal or ammonium carboxylate in an amount in excess over the amount needed to neutralize the sulfonic acid group(s) and any free or complexed SO.sub.3 present in the product mixture from the sulfonation reaction. ##STR6##
Treatment of alkyl esters of carboxylic acids with sulfonating agents followed by neutralization is known in the art to result in the formation of a variety of products, the nature of which is determined by the specific conditions which ar employed for the reaction. The sulfonation reactions of alkyl esters of carboxylic acids have been reviewed by B. L. Kapur et al. in Journal of the American Oil Chemists' Society, 1978, 55 (6), pp. 549-557, and by E. E. Gilbert in "Sulfonation and Related Reactions", Interscience Publishers, Wiley & Sons, Inc., NY, 1965, p. 36, the teachings of which are incorporated herein by reference. In general, these reactions result in the formation of products arising from alpha sulfonation and/or cleavage of the ester as illustrated generically in Equation 2 for sulfonation of a fatty acid methyl ester with sulfur trioxide followed by neutralization with sodium hydroxide. The mechanism of these reactions has recently been discussed by B. Fabry and B. Giesen in Tenside Surf. Det., 1990, 27(4), pp. 243-248, the teachings of which are incorporated herein by reference. ##STR7##
Due to the utility of alpha sulfonated esters as surfactants, there has been considerable interest in the development of processes which lead to the predominant formation of the alpha sulfonated esters of formula (VII); however, it has been proven to be difficult to avoid the formation of the dialkali metal salts of formula (VIII). By way of example, European Patent Application 153,016 describes a process for producing esters of formula (VII) which contain low levels of disalts of formula (VIII).
The sulfonation of phenyl esters of alkanoyloxyacetic acids of formula (II) does not appear to be known in the art. In addition, it is not clear from available references whether these diesters will undergo: (1) ring sulfonation reactions typical of phenyl esters, (2) alpha sulfonation and ester cleavage reactions typical of alkyl esters, or (3) some combination of these reactions. It has now been found that diesters of formula (II) can be sulfonated with selectivity for ring sulfonated products of formula (III). It has further been found that the products of formula (III) can be neutralized to give benzenesulfonate salts of formula (I).